Two types of genetic recombination events will be studied using defined in vitro systems and purified proteins derived from bacteria and yeast. The proteins to be studied are: 1) The FLP protein of the yeast 2 micron plasmid. This protein promotes a site-specific recombination event which results in the inversion of a segment of the 2 micron plasmid DNA relative to the rest of the plasmid. 2) The recA protein of E. coli. This protein plays a central role in homologous or general genetic recombination in bacteria. The long range goal of this project is to elucidate the chemical mechanisms by which these and similar proteins promote genetic recombination. The work will employ the full range of chemical, kinetic, physical, and genetic techniques available for biochemical analysis. The health relatedness of this work derives from the importance of genetic recombination in many basic biological processes. Especially important in this regard is the central role of genetic recombination events in the generation of antibody diversity and in transformation of mammalian cells by a number of DNA tumor viruses.